Quick change precisor

ABSTRACT

A precisor plate for an automatic wire bonder having a heat block attachment portion thereon to precisely attach a heat block thereto provides a simple and quickly adjustable precisor plate and method of alignment. The precisor plate includes fixed alignment pins to align the precisor plate relative to a lead frame in an automatic wire bonding machine. In a preferred embodiment, the heat block is integral with the precisor plate and includes internal bores and or passageways for receiving a heating element, a thermocouple, and/or a vacuum source.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/862,238, filed May 22, 2001, pending, which is a continuation ofapplication Ser. No. 09/333,080, filed Jun. 14, 1999, now U.S. Pat. No.6,237,830, issued May 29, 2001, which is a divisional of applicationSer. No. 08/794,877, filed Feb. 5, 1997, now U.S. Pat. No. 5,971,256,issued Oct. 26, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to work stations or work holdersused in indexing semiconductor lead frames through an automatic wirebonder and, more specifically, to a precisor plate employed in such awork holder or work station adapted to be quickly readjustable toaccommodate differently configured lead frames.

[0004] 2. State of the Art

[0005] There are a limited number of companies in the semiconductorindustry that manufacture automatic wire bonders used to form wire bondson semiconductor devices. A leading manufacturer of such wire bondingmachines is Kulicke and Soffa Industries, Inc. of Willow Grove, Pa.,manufacturer of a work holder designated as model number 2810. Theseautomatic wire bonders typically employ dedicated work holders which areadapted to receive a specifically configured lead frame. The workholders are coupled to or connected to at least three mechanical drives,one for advancing the lead frame, one for positioning the lead frame onthe bonding station and one or more drives for clamping the lead framein the station. Heretofore, changing the work holder required skilledtechnicians to disassemble and reassemble or partially rebuild the workholder to accommodate each differently configured lead frame and ensurethat the new, differently configured lead frames will be preciselyaligned with respect to the wire bonder. Such a reconfiguration processtypically takes an hour or more with current work holders.

[0006] A typical work holder for a Kulicke and Soffa wire bondingmachine includes a box-like frame attached to the machine through whichlead frames are indexed, the box-like frame forming part of the workstation at which lead frames are wire bonded. In addition, a precisorplate is attached to a vertical slider, the slider vertically moving theprecisor plate beneath the lead frame. The precisor plate, inconjunction with a heat block, typically rectangular in shape, supportsthe lead frame in the work holder and keeps the lead frame from movingduring the wire bonding operation.

[0007] An attempt to provide a modular work station or work holder whichis easily removed from and replaced in an automatic wire bonder isdisclosed in U.S. Pat. No. 4,765,531 ('531 patent) assigned to Kulickeand Soffa Industries, Inc., the manufacturer of the aforementioned model2810 wire bonder. While the '531 patent is generally described withrespect to Kulicke and Soffa automatic wire bonder models 1481 and 1482,many of the components and their configurations are similar to thecomponents of the model 2810 wire AH bonder. In the '531 patent, theproblem of precisely aligning the precisor plate and heat block relativeto the rest of the work holder is addressed by immobilizing the entirework station while various pins and bolts align and secure thesecomponents together and to the wire bonding machine. While the quickchange work station described in the '531 patent may have been animprovement over the work holder stations of its time, the '531 patentwork holder requires separate alignment of both the precisor plate andthe heat block.

[0008] The work holder that is provided by Kulicke and Soffa with the2810 model is as difficult, if not more, to align than the work holderdescribed in the '531 patent. In addition to not providing a workstation that can be quickly realigned, the precisor plate provided withthe 2810 model wire bonder has moveable pins that must themselves beproperly aligned to precisely engage tooling holes in the lead frame. Inaddition, the heat block must be separately aligned, and the precisorplate itself requires planarity adjustment, both right-to-left andfront-to-back.

[0009] When a wire bonder as herein described is out of service,production on that machine is lost, resulting in a decrease inmanufacturing efficiency. Accordingly, in order to avoid down time forrealignment of the work holder, such automatic wire bonders are kept online as long as possible, wire bonding similarly configured lead frames.In order to accommodate low production items, where only a few partsmust be wire bonded, intermittent batch production, where theconfiguration of the wire bonder is frequently changed, or longproduction runs, where realignment of the precisor plate must beperiodically performed, it would be desirable to provide a quick changeprecisor plate that can be simply and quickly adjusted.

BRIEF SUMMARY OF THE INVENTION

[0010] Accordingly, a precisor plate and method of aligning the precisorplate to an automated wire bonding work station is herein disclosed. Afirst embodiment of the precisor plate in accordance with the presentinvention comprises a plate having fixedly attached alignment pinspositioned to engage tooling holes in a lead frame or lead frame strip,whether stamped, etched or otherwise manufactured, and a heat blockattachment or mounting portion on the plate for attachment of a heat-block thereto. The heat block is held in precise position relative tothe precisor plate by a pin which extends from the heat block mountingportion into the heat block and an abutment surface adjacent the heatblock mounting portion against which the heat block must abut in orderto fit onto the pin. The heat block is secured to the heat blockmounting portion by threaded screws which fit through holes provided inthe heat block mounting portion and into matingly threaded holes in theheat block.

[0011] In another preferred embodiment, at least two pins are providedon the heat block mounting portion and engage an equal number of pinholes in the heat block. The pin holes, which have an internalconfiguration to substantially match the outer configuration of thepins, must engage with the pins and thus properly align the heat blockto the precisor plate.

[0012] In yet another preferred embodiment of a precisor plate inaccordance with the present invention, the precisor plate and heat blockcomprise a one-piece component such that the heat block is eitherpermanently attached to the precisor plate or integrally formed as partof the precisor plate. Such a device removes entirely the need to alignthe heat block relative to the precisor plate, or to separately alignthe heat block to the work station.

[0013] The heat block according to the present invention may be providedwith various internal passages, in addition to those used for securingpurposes. Such internal passages may include bores sized to receiveheating elements, temperature measuring devices, such as thermocouples,and passages to provide a vacuum at the wire bonding surface of the heatblock to help secure the lead frame relative to the heat block duringthe wire bonding process.

[0014] In order to align and attach a precisor plate of the presentinvention to a work station, the heat block is attached to the precisorplate (if separate components) and the precisor plate is attached to avertical slider of the wire bonding machine by inserting screws throughholes provided in the precisor plate and into threaded holes provided inthe slider. A lead frame is then indexed into the work station. Beforetightening these screws into the threaded holes in the slider, theprecisor plate is moved until, upon-actuation of the slider, thealignment pins of the precisor plate engage the tooling holes of thelead frame without disturbing the position of the lead frame. When thealignment pins can be engaged into the tooling holes without lifting(i.e., disturbing) the lead frame, the precisor plate is in the correctposition and can be securely attached to the slider by tightening thescrews into the slider.

[0015] To facilitate movement of the precisor plate relative to the workstation, one or more holes may be formed in the precisor plate intowhich grasping members, such as pins or threaded screws, may beinserted. These grasping members may be grasped by a user to move theprecisor plate relative to the work station. After proper alignment andupon securement of the precisor plate relative to the work station, thegrasping members may be removed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016]FIG. 1A is an isometric exploded view of a first embodiment of aprecisor plate in accordance with the present invention positionedwithin a work station of a wire bonding machine;

[0017]FIG. 1B is an isometric top view of the precisor plate of FIG. 1A;

[0018]FIG. 1C is an isometric bottom view of the precisor plate of FIG.1A with an associated heat block;

[0019]FIG. 2 is an isometric top view of a second embodiment of aprecisor plate in accordance with the present invention;

[0020]FIG. 3A is an isometric top view of a third embodiment of aprecisor plate in accordance with the present invention;

[0021]FIG. 3B is an isometric bottom view of the precisor plate of FIG.3A; and

[0022]FIG. 4 is a side cut-away view of the precisor plate of FIG. 1Apositioned within the work holder and attached to a wire bondingmachine.

DETAILED DESCRIPTION OF THE INVENTION

[0023]FIG. 1A illustrates a precisor plate 10 in accordance with thepresent invention positioned within a modular, box-shaped work station12 known in the art. The work station 12 is comprised of a bottom plate14 having a pair of rail guides 16 and 18 consisting of longitudinallyextending steps providing abutting edges 20 and 22 against which a pairof side rails 24 and 26 can be positioned, respectively. The tops 28 and30 of the side rails 24 and 26 are also provided with longitudinallyextending abutment surfaces 32 and 34 for holding a top plate 36 alongsimilarly configured longitudinally extending abutment surfaces 38 and40 of the top plate 36. The top plate 36 is provided with a first majoropening 42 defined in the top surface 44 of the top plate 36. Theopening 42 provides access to the lead frame and die (not shown) thatare to be wire bonded by a wire bonding head of a wire bonding machineto which the work station 12 is attached. Other apertures or openings46, 47, 48, and 49 defined in the top plate 36 may also be provided forpositioning and/or access purposes.

[0024] The side rail 26 defines an opening 50 therein large enough toreceive the precisor plate 10 and allow vertical movement of theprecisor plate 10 within the opening 50. When assembled, the workstation 12 in conjunction with the precisor plate 10 helps to providephysical, immobile support for a lead frame during the wire bondingprocess to ensure that the lead frame does not move. In addition,movement of the precisor plate 10 relative to the work holder 12 isprovided to allow lead frames to be indexed into and out of the workstation 12.

[0025] As better illustrated in FIGS. 1B and 1C, the precisor plate 10is a one-piece component comprised of a plate 60 having a heat blockattachment portion or ledge 62 depending therefrom, the ledge 62 havinga top surface 64 on a different horizontal plane than a top surface 66of the plate 60. A heat block abutment surface 68 is provided betweenand substantially perpendicular to the plate 60 and the ledge 62. Inorder to attach a heat block 69 to the precisor plate 10 and properlyposition it relative to the precisor plate 10, holes 70 and 72 areprovided in the ledge 62 configured to match the position of threadedholes 74 and 76 in the heat block 69. The holes 70 and 72 are spacedfrom the abutment surface 68 substantially the same distance as theholes 74 and 76 are spaced from the abutment side 82 of the heat block69. In addition, a pin 78 attached to the top surface 64 of the ledge 62is positioned to engage pin hole 80 in the heat block 69 with the pin 78being spaced from the abutment surface 68 substantially the samedistance the pin hole 80 is from the abutment side 82. Accordingly, thecombination of abutting the abutment side 82 of heat block 69 againstthe abutment surface 68 and engaging the pin 78 into the pin hole 80results in a properly positioned and aligned heat block 69 relative tothe precisor plate 10. Threaded screws (not shown), as known in the art,can then be inserted through holes 70 and 72 and engaged with threadedholes 74 and 76, respectively, so that the heat block 69 is immobilizedin proper alignment relative to the precisor plate 10.

[0026] The ledge 62 also defines a semicircular opening 110 to allowaccess through the ledge 62 to the opening 112 of internal bore 114 inthe heat block by the wire bonding machine, as will be further describedwith reference to FIG. 4.

[0027] The plate 60 of the precisor plate 10 is also provided with otherholes, both threaded and unthreaded. For example, holes 84 and 86 aredefined through the plate 60 to attach the precisor plate 10 to a wirebonding machine. In addition, holes 88 and 90 are positioned tosubstantially match the spacing of tooling holes provided in a leadframe strip as is known in the art. Alignment pins (see FIG. 4) can thenbe secured into the holes 88 and 90. Other holes 92, 94, and 96 arepositioned about the top surface 66 of the plate 60 into which agrasping member such as a threaded fastener 98 can be attached, if holes92, 94, and 96 are internally threaded, or a pin 100 sized to match thesize of the holes 92, 94, or 96 if holes 92, 94, and 96 are notthreaded. The threaded fasteners 98 and/or pins 100 can be grasped tomove the precisor plate 10 to the work station 12 while aligning theprecisor plate 10 to the work station 12, as will be subsequentlydescribed. After proper alignment of the precisor plate 10, the threadedfasteners 98 and/or pins 100 can be removed from the precisor plate 10and are not otherwise necessary for the wire bonding process.

[0028] It is also contemplated, as illustrated in FIG. 2, that multiplepins 118 and 119 or other positioning members such as raised and/orrecessed portions may be employed to align a heat block 113 to aprecisor plate 115 of the present invention so that, in contrast to theconfiguration shown in FIG. 1B, the abutment surface 68 and ledge 62 arenot required. Accordingly, such a precisor plate 115 could be formedfrom a plate 116 having a top surface 117 in a single plane with theheat block 113 attached directly to the top surface 117 of the plate116.

[0029] Referring now to FIGS. 3A and 3B, another preferred embodiment ofa precisor plate 120 according to the present invention is illustrated.Similar to the precisor plate 10 of FIGS. 1A, 1B and 1C, the precisorplate 120 is comprised of a single element 122. The heat block 124,however, is integral with the single element plate 122 and may be formedas a single piece with the precisor plate 120. The heat block 124 may beprovided with various passages such as an internal bore 126 extendingtherein and sized to receive a heating element (not shown) in amale/female relationship. A hole 128 may also be provided proximate theopening 130 of the internal bore 126 to which the heating element (notshown) may be secured. As shown in FIG. 3B, the heat block 124 may alsoinclude another bore 132 therein into which a thermocouple (not shown)can be inserted to monitor the temperature of the heat block 124.Referring again to FIG. 3A, the top surface 134 of the heat block 124may also have a pair of vacuum outlet ports 136 and 138 through which avacuum may be drawn to assist in immobilizing a lead frame until theheat block 124 abuts the top plate 36 (see FIG. 4). Referring again toFIG. 3B, in the bottom surface 140 of the heat block 124, a vacuum inletport 142 in communication with vacuum outlet ports 136 and 138 can beattached to a vacuum source of a wire bonding machine.

[0030]FIG. 4 illustrates the precisor plate 10 attached to a wirebonding machine 150 known in the art. A lead frame 152 is in a bondingposition within the work station 12 with the heat block 69 holding thelead frame 152 against the bottom surface 154 of the top plate 36.Alignment pins 153 engage the index or tooling holes 155 in the leadframe 152.

[0031] After being clamped in position by the heat block 69, the leadframe 152 is further supported by an air cylinder 157 which is locatedinside a center frame 166 of the wire bonding machine 150 and whichengages the heat block 69. The additional force provided by air cylinder157 further stabilizes the heat block 69 so that the lead frame 152 ismore solidly held in the wire bonding machine 150. In addition, the aircylinder 157 may provide a vacuum source 159 to the heat block 69through internal passages (not shown) in the air cylinder 157 connectedto a vacuum outlet (not shown) in the wire bonding machine 150 so that,as previously described, the lead frame 152 is held in position relativeto the heat block 69 until the heat block 69 abuts the top plate 36.After the bonding operation, drive rollers (not shown), as are known onsuch wire bonding machines, actuated by the wire bonding machine 150move the lead frame 152 to the next index position once the alignmentpins 153 are lowered out of the index holes 155 of the lead frame 152.

[0032] The precisor plate 10 is attached by screw 156 and lock washer158 to vertical slider 160 that vertically moves the precisor plate 10up and down relative to the work station 12. The slider 160 is mountedfor movement on a movable front member 168 which is locked in place by asplit clamp 170 and screw 172. The front frame member 168 is movable ona pair of shaft members 174 (only one of which is shown) and, whenproperly indexed by a set screw 176 engaging a side edge of the bottomplate 14, positions both the front frame member 168 and the slider 160in the proper operating position. Similarly, the rear frame member 178is movable on the same shaft members 174, which is a part of the base ofthe automatic wire bonder, and is set in place by set screws 180engaging the bottom plate 14. There is also provided a split clamp 182and screw 184 to hold the rear frame member 178 in place. The heat block69 is attached to the ledge 62 of the precisor plate 10 by screw 162 andlock washer 164 and further held in position by pin 78.

[0033] In practice, the work station 12 is first mounted on the centerframe 166 and the precisor plate is attached to the slider 160. Thescrew 156 is tightened enough to hold the precisor plate to the slider160 but is loose enough to allow movement of the precisor plate 10relative to the slider 160. In a lowered position and with the top plate36 removed, the precisor plate 10 is moved relative to the slider 160until alignment pins are positioned proximately below the tooling orindex holes 155 of the lead frame 152. Grasping members such as threadedfasteners 98 and/or pins 100 as illustrated in FIG. 1A may be employedto assist movement of the precisor plate 10. The precisor plate 10 isthen raised by the slider 160 to ensure that the alignment pins 153 donot substantially disturb the position of the lead frame 152. Typically,such disturbance can be detected by observing vertical movement of thelead frame 152 by the alignment pins 153. If the alignment pins 153 donot precisely engage the indexing holes 155 of the lead frame 152, theprecisor plate 10 can be adjusted until the alignment pins 153 fit(i.e., ±1 mil between the centers of alignment pins 153 and index holes155) within the index holes 155 without lifting the lead frame 152. Oncethe precisor plate 10 is in position, the screws 156 can be tightened tosecure the precisor plate 10 relative to the rest of the work station12.

[0034] It is noted that other configurations of modular work stationsmay also be employed in accordance with the precisor plate 10 of thepresent invention. Thus, while a modular work station as hereindescribed has been shown with respect to a Kulicke and Soffa Industries,Inc. wire bonding machine, it is contemplated that a precisor plate inaccordance with the present invention may be adapted to and/or utilizedwith other wire bonding machines and work stations known in the art.Those skilled in the art will also appreciate that various combinationsand modifications of the preferred embodiments may be made withoutdeparting from the spirit of this invention and the accompanying claims.

What is claimed is:
 1. A work holder in a wire bonding machine, comprising: a bottom plate having a first rail guide at a first side and a second, parallel rail guide at a second side; a first side rail and a second side rail, said first side rail engaging said first rail guide and said second side rail engaging said second rail guide, said second side rail defining a precisor plate receiving opening therethough; a top plate having a bottom surface received on said first and second side rails; a vertical slide positioned proximate said second side rail; a precisor plate attached to said vertical slide and extending through said precisor plate receiving opening; and a heat block attached to said precisor plate having a top surface positioned below to said bottom surface of said top plate.
 2. A heat block for a wire bonding machine having a precisor plate attached thereto, comprising: a heat block having an attachment surface defining at least one precisor alignment member receiving portion and an abutment surface for abutting a surface of the precisor plate.
 3. A kit for a precisor plate used in a wire bonding machine, comprising: a precisor plate having a heat block attachment portion thereon; a heat block for attaching to said heat block attachment portion; and a pair of alignment pins to be fixedly attached to said precisor plate and spaced to engage tooling holes in a lead frame.
 4. A method of wire bonding a first plurality of lead frames and a second plurality of lead frames, each having indexing holes therein, comprising: wire bonding a first plurality of lead frames with a wire bonding machine having a precisor plate in a first position, the precisor plate having at least two alignment pins attached thereto; changing the position of the precisor plate by loosening the precisor plate from the wire bonding machine so that the precisor plate can be moved relative to the slider; raising the precisor plate until the at least two alignment pins of the precisor plate engage the indexing holes of the lead frame; moving the precisor plate relative to the lead frame until the at least two alignment pins precisely engage the indexing holes of the lead frame without substantial contact with the lead frame; fastening the precisor plate to the wire bonding machine; and wire bonding a second plurality of lead frames. 